Optical articles that provide good imaging qualities while reducing the transmission of incident light into the eye are needed for a variety of applications, such as sunglasses, vision correcting ophthalmic lenses, plano lenses and fashion lenses, e.g., non-prescription and prescription lenses, sport masks, face shields, goggles, visors camera lenses, windows, automotive windshields and aircraft and automotive transparencies, e.g., T-roofs, sidelights and backlights. Responsive to that need, photochromic plastic articles used for optical applications have been given considerable attention. In particular, photochromic ophthalmic plastic lenses have been of interest because of the weight advantage they offer, vis-à-vis, glass lenses.
Photochromic plastic articles have been prepared by incorporating the photochromic material into the plastic substrate by surface imbibition techniques. In this method, photochromic dyes are incorporated into the subsurface region of a plastic article, such as a lens, by first applying one or more photochromic dyes/compounds to the surface of the plastic article, either as the neat photochromic dye/compound or dissolved in a polymeric carrier or organic solvent carrier, and then applying heat to the coated surface to cause the photochromic dye/compound(s) to diffuse into the subsurface region of the plastic article (a process commonly referred to as “imbibition”). The plastic substrates of such photochromic plastic articles are considered to have sufficient free volume within the polymer matrix to allow photochromic compounds to transform from the colorless form into the colored form, and then revert to their original colorless form.
There are, however, certain polymer matrices that may not to have sufficient free volume to allow the aforedescribed electrocyclic mechanism to occur sufficiently to permit their use as a substrate for imbibed (or internally incorporated) photochromic materials for commercially acceptable photochromic applications. Non-limiting examples of such substrates include thermoset polymer matrices, such as those prepared from allyl diglycol carbonate monomers, e.g., diethylene glycol bis(allyl carbonate), and copolymers thereof; the commonly known thermoplastic bisphenol A-based polycarbonates; and highly cross-linked optical polymers.
To allow the use of thermoset polymers, thermoplastic polycarbonates, and highly cross-linked optical polymeric materials as plastic substrates for photochromic articles, it has been proposed to apply photochromic coatings to the surface of such plastic substrates. It has been an ongoing challenge to minimize the amount of time needed to activate and deactivate the photochromic materials contained in the coatings, in response to consumer demands.